A vast number of complex digital systems are sequential in nature, i.e., the next state of the system depends not only on the applied inputs, but upon the past history of events as well. A familiar and simple example of such a device is a digital clock, in which each time pulse advances the system to a new and different state until a predetermined counting modulus has been exceeded. More complex representatives in this class include increasing amounts of electronic ordnance, among which are underwater mines and sophisticated fuzes.